Speaking from a purely hypothetical within the theme of Zombie uprising, any assault weapon would be a bad idea.

I can't quote the Zombie Survival Guide because I don't have it handy but...

A zombie can only be killed with a headshot. Fully automatic weapons are are both impractical and a waste of ammo when that's considered.

Also, if there were such an event, martial law would be very likely (see any zombie movie for example). If you were walking down the street with either of those you'd draw a lot of attention from the military types...the wrong kind of attention.

The best kind of weapon is the one that can be used to fire an accurate shot to the head of a zombie, is very reliable, isn't tactical, and uses a cartridge which is very common...like a hunting rifle...though there are other options.

If you can get your hands on the book it's a very good read...as is the sequel, World War Z. It does a really good job of putting the human perspective into the topic. Many of what Max talks about in his book could apply to any pandemic. Ever since the Avian Bird Flu became a hot topic around here (and since my SAR organiziation became part of the provincial pandemic response plan) I've taken a bit of an interest in such things and the parallels are very interesting.